Role of Sockets in IC Product Life Cycle
Ila Pal, Ironwood Electronics
Introduction:
Introduction:
For over half a century, the semiconductor industry has been governed by a
commonly known principle described as Moore’s Law. This “law” predicts that
through technological advancement a doubling of the number of transistors per
integrated circuit will occur within a given geometric area on regular 18 month
intervals. The realization of this doubling effect over time has resulted in an
ever-widening range of semiconductor (IC) devices exhibiting increases in
functionality and processing speed combined with an increased demand for
power and effective thermal management. This doubling effect has also driven a
matching rapid evolution in IC package types and I/O interface configurations.
Typical IC starts with concept/prototype phase, moves to design validation
phase, leaps into application development phase, rides into production phase and
ends with upgrade/replacement phase (Figure 1). During these phases innovative
interconnects have kept pace with the rapid evolution in semiconductor
technology. IC sockets have been developed for a complete range of
performance requirements and I/O configurations for each of those phases. This
article will describe form, fit and function of IC sockets requirement in each of
those phases.
Figure 1 – Five stage IC product life-cycles
Concept/Prototype Phase:
The important step in this phase is to verify whether the prototype functions as
per the design intent. Since there can be revisions to the IC, an IC socket in the
development board helps to avoid solder/de-solder routine of the precious
device. The IC socket plays a major role in determining whether the device met
design intent or not. Because of these criteria, the IC socket has to be carefully
selected. The number one factor is bandwidth. Because the IC has to perform
certain functions at specific speed, the signal loss has to be minimal. Since
additional socket interface is introduced in the signal loop, either the socket has
to have sufficient bandwidth to pass signal without insertion/return losses or the
socket specifics has to be de-embedded in the functional verification. Since it is
very complex to de-embed specific parameter, safer solution is to find a socket
with higher bandwidth. Next to bandwidth, DC series resistance plays important
role. Socket technology that can provide low and consistent contact resistance is
preferable to avoid false failures. The next factor is current carrying capability.
An image sensor may require a low current such as 100mA to 200mA per ball
whereas a power management device may require 3A to 5A per ball. Socket
contact technology that accommodates this requirement has to be selected
properly. The next critical factor is contact technology compliance. Because the
devices have wide co-planarity, the contact technology chosen has to
accommodate the flatness variations. One more factor plays significant role in
prototype stage is temperature requirement. Various socket contact
technologies available for this market include embedded wire-on elastomers,
plated flex circuit capped elastomers, diamond particle interconnects (Figure 2),
stamped contacts, spring contacts, hybrid contacts and other variations. Also
socket features such as small footprint, easy chip replacement, easy mounting
methodology, moving socket from board-to-board and low cost are must for this
market.
Figure 2 – 40GHz, Small footprint, Diamond particle interconnect socket
Design Validation Phase:
In this phase, a typical IC goes through many kinds of environmental tests.
Typical tests include thermal shock, temperature cycling, humidity exposure,
vibration test, salt spray and other tests based end usage. Validation is required
to verify whether IC performs in all environments. Socket contact requirements
such as air tight connection (low and consistent contact resistance), repeated
cycles, temperature extremes, wear, cleaning plays top role. Socket features
which are used in prototype stage are not relevant for this validation stage. In
this stage, robust lid, tight latching, permanent mounting and extremely low cost
because of one time usage are factors that satisfies this market.
Application Development Phase:
Now that IC function was proved and it is capable of withstanding end user
environments, the next step is to develop application software for the IC.
Sockets that are used in prototype stage will satisfy the requirements of
application development stage as the need is to simply swap devices during the
software development process. Since the performance is verified by executing
software routines, the socket contact technology should accommodate high
bandwidth, low signal loss, low contact resistance and appropriate current flow
capability. Since the devices are not swapped frequently, socket lids can be
screw mounted as opposed to easy open latch to reduce overall cost of test.
Production Phase:
This is a key stage of any IC’s life. After verification and development, customer
agrees to buy those ICs in millions. When the ICs are fabricated, it needs to be
tested before shipped to customer. Various tests such as burn-in, functional,
fuse test, failure analysis, etc happens in this production phase. All ICs go
through burn-in and functional test. A typical ICs life is exemplified by bath tub
curve. Because of inherent nature of IC manufacturing processes, few
percentage of ICs fail very early in their life and the failure is very minimal
during its life time and then failure percentage goes up at end of their life. Burnin tests are conducted to screen those early failures. Typical burn-in test
includes testing IC device at 125C for 8 hrs. If the IC passes this test which
means it is ready for primetime. Typical socket requirements are high
temperature and high insertion/extraction cycles. Since millions of manufactured
ICs go through this burn-in test, more sockets are needed which drives the cost
to extremely low. Socket technology using molded housing and low cost stamped
contact satisfies burn-in test market
After passing burn-in test, these ICs go through functional test which is often
called production test. Since function is verified at this stage, bandwidth and
current capacity requirements ranked high. Since millions of devices are being
tested, higher the insertion/extraction cycle count, lower the overall cost of test.
Spring pin sockets (Figure 3) dominate this production test market.
Figure 3 – 500K cycle, High endurance spring pin socket with removable
clamshell lid
Upgrade/Field
Upgrade/Field Replacement Phase:
After production test, the devices either soldered to the board or sometimes
placed inside the socket for replacement with future IC that has upgraded
functions. These sockets are very similar to validation stage sockets which are
more robust with few insertion/extraction requirements and costs fraction of a
dollar in volume. Sockets (Figure 4) made out of FR4 with screw machined
contacts are prevalent for this market.
Figure 4 – Low cost field upgrade socket
Conclusion:
A single contact technology cannot satisfy all requirements for IC verification
throughout its life cycle. Selecting a socket that has replaceable modules of
different contact technologies to accommodate all the test requirements of IC
life cycle is a fruitful solution. Socket footprint defines component proximity to
IC. Series resistors, capacitors, tuning inductors and others need to be placed
minimal distance from IC in GHz applications. Socket footprint is important in
Concept/Prototype, Design Validation, Application Development and
Upgrade/Field Replacement phases if the bandwidth requirements are in GHz
range. Also socket footprint standardization will pave way for overall low cost of
test per IC life cycle.
Author:
Mr. Ila Pal is VP of Marketing at Ironwood Electronics can be reached at
ila@ironwoodelectronics.com